Wastewater Wetland Assimilation: Climate Change Mitigation in New Orleans
Sarah K. Mack*, John W. Day**, R. Lane**, J. Funk***
* Tierra Resources LLC, 1320 St. Andrew Street Suite 6, New Orleans, Louisiana 70130 USA
** Department of Oceanography and Coastal Sciences, Louisiana State University Baton Rouge, Louisiana 70803 USA
***Environmental Defense Fund, 1875 Connecticut Ave NW #600, Washington D.C. 20001 USA
Keywords: climate change mitigation; carbon sequestration; wetland treatment
The East Bank Sewage Treatment Plant (EBSTP) is located in the lower 9th Ward of New Orleans near Bayou Bienvenue. The EBSTP provides wastewater treatment for the entire east bank of Orleans Parish and treats biosolids for both the east and west banks of Orleans Parish. The treatment facility received approximately $70 million of damage as a result of the 17-foot storm surge created by Hurricane Katrina. The neighboring St. Bernard Parish received catastrophic damage to all seven wastewater treatment plants. In addition to restoring critical infrastructure, both agencies faced upcoming regulatory nutrient limits which would require new energy intensive tertiary treatment systems. The municipalities sought a solution to climate change and energy scarcity adaptation that would provide a less expensive option to restore infrastructure while enhancing deteriorating coastal marshes as a self-sustaining complement to the structural protection of levees.
Currently nutrient rich effluent from both parishes is discharged to the Mississippi River where it contributes to hypoxia in the Northern Gulf of Mexico. Rerouting the effluent will significantly reduce energy requirements for pumping and conveyance and allow the nutrients to be used to replenish the wetlands, rather than increasing damage to the coastal environment. Most of the degraded wetlands are within the rural St. Bernard Parish that produces a dry weather flow of approximately 38,000 m3 a day. The EBSTP produces a dry weather flow averaging 340,000 m3 a day. Hurricane Katrina presented the opportunity for the two parishes to partner to pursue wetland assimilation of secondarily treated wastewater effluent as an alternative to conventional tertiary treatment and hurricane protection. The application of municipal effluent will buffer saltwater intrusion, offset regional subsidence, and re-establish favorable conditions for bald cypress growth. This type of wetland restoration promotes additional carbon sequestration by reversing wetland loss, enhancing burial, and by reestablishing cypress forests. Thus, the wetland assimilation project will integrate sustainability with mitigation measures by enhancing storm surge protection, utilizing natural energies, and sequestering large amounts of carbon.
There is a rising demand to know how much carbon is sequestered by wetlands, the timeframe in which it takes place, and the amount of carbon emitted during wetland loss. To answer these questions an analysis was conducted based upon peer-reviewed literature to identify the carbon storage pools of wetlands and to quantify the primary carbon storage mechanisms where carbon sequestration is being enhanced by wetland assimilation of municipal effluent (Rybczyk et al. 2002; Day et al. 1999). In addition to peer-reviewed literature, the analysis utilized non-published data collected as part of monitoring programs by state agencies, as well as data collected by university scientists. The objective of the analysis was to calculate general long-term (e.g., 50+ years) carbon sequestration rates for wetland restoration inclusion in greenhouse gas (GHG) policy regimes. The findings were then applied to the regional wetland assimilation system planned to receive municipal effluent from the city ofNew Orleansin order to quantify the carbon sequestration of an 809 hectare restoration area and the full 12,140 hectares as applicable towards carbon credits (Table 1.1).
Table 1.1. Additional Carbon Sequestration (CO2e) for theOrleans Wetland Assimilation System
|Mechanism||809 ha||12,140 ha|
|Biosequestration in planted cypress a year||22,000 tons||334,000 tons|
|Total additional 1st year||36,000 tons||534,000 tons|
|Total additional 50th year||74,000 tons||1,106,000 tons|
|Total cumulative additional over 50 years||2,915,000 tons||43,732,000 tons|
The results of this research can be used as a predictive tool for utilizing carbon credits to fund the municipal effluent wetland restoration project. The methodology for quantifying the carbon sequestration potential of the project provides guidance to others pursuing innovative climate mitigation measures that integrate natural resource management with wastewater treatment. The paper concludes with a detailed summary of future research requirements to provide the scientific basis for quantifying carbon sequestration and certifying offsets from wastewater wetland projects.
Addressing global climate change will require a significant reduction in annual GHG emissions in the United States and throughout the world. The management approaches developed to restore and sustain theNew Orleansregion will provide insight to those elsewhere needing to adapt to climate change in times of resource scarcity. Natural sinks such as wetlands that capture and store carbon from fossil fuels will have an important role in a new low-carbon economy. Using natural wetlands for tertiary treatment becomes a multi-benefit climate change adaptation measure by sequestering large amounts of carbon, offsetting sea level rise, and increasing the resiliency of the natural and built environment to hurricanes.
Day, J. W., J. Rybczyk, F. Scarton, A. Rismondo, D. Are, and G. Cecconi. (1999) Soil accretionary dynamics, sea-level rise and the survival of wetlands in Venice Lagoon: a field and modelling approach. Estuarine, Coastal and Shelf Science 49:607-628.
Rybczyk, J., J. Day, and Conner W. (2002) The impact of wastewater effluent on accretion and decomposition in a subsiding forested wetland. Wetlands. 22:18-32.